Three to four million persons in the United States suffer from glaucoma to some degree, although only about half of these persons are treated by routine administration of glaucoma medication. Glaucoma is recognized to be the leading cause of blindness in this country.
Typical treatment for glaucoma to reduce the excessive intraocular pressure involves the administration of drugs which operate on the intraocular pressure. These drugs do not have a long term straight line effect on intraocular pressure, however, and individual treatments may be more or less effective at any particular period of time in the treatment cycle. For most glaucoma cases, intraocular pressure varies throughout the day, usually reaching its peak about 3:00 am. This diurnal cycle presents difficulties to the attending physician, who sees the patient at only one relatively short period of time. For this reason, it is difficult for the practitioner to accurately assess the effect of glaucoma medications.
At the present time, there is recognition that the cycle of intraocular pressure is diurnal and is subject to several variables. However, no acceptable means presently exists to continuously measure intraocular pressure.
One such means has been proposed in U.S. Pat. No. 4,089,329, to Couvillon et al, in which a contact lens is used to maintain vision for the patient. The patent notes, however, that sensitivity of the cornea to the device presents a serious problem. To solve this problem, a miniature strain gauge pressure transducer is used, in the form of a noncompliant, planar diaphragm for applanating a small portion of the sclera. A hydrogel ring is placed within the conjunctival cul-de-sac of the eye in a concentric orientation with the cornea to permit vision during the process.
In the Couvillon et al device, separation of tissue supplies the necessary force to the transducer diaphragm to applanate the contacted portion of the sclera. The resultant stress, monitored as resistance variations, is sent to a transmitter via connecting wires. While the Couvillon et al patent does not say so explicitly, the wires appear to extend from the hydrogel ring to a transmitter which is external to the eye. Signals are sent to a receiver/transcriber for analysis and use in other ways.
The Couvillon et al device contemplates the use of a ring platform, made preferably from hydrogel. The ring must be sufficient to allow eye movement without serious contact with corneal tissue. Wire conductors convey the current from the strain gauges, and change in resistance is measured as change in voltage. As noted in the description of the "communicating means" described in the Detailed Description of the Couvillon et al patent, the transmitter is fixed to the patient's glasses or person. Presumably, preventative methods are in place to prevent the patient from removing his or her glasses with the ring platform still in the eye and attached to the transmitter via the wire conductors.